BALLYAGRAN PUBLIC SUPPLY GROUNDWATER SOURCE PROTECTION ZONES Jenny Deakin Groundwater Section Geological Survey of Ireland December 1995 BALLYAGRAN PUBLIC SUPPLY 1. SUMMARY OF WELL DETAILS GSI no. : 1411NWW035 Grid ref. : 14701 12808 Owner : Limerick Co. Co. Well type : Borehole Elevation (top of casing) : 103.47 m OD (Poolbeg). Ground level is 104.38 m OD. Depth : 35.36 m Depth of casing : 17.37 m Diameter : 200 mm (8") Depth-to-rock : estimated to be between 13 and 16 m Static water level : 7.35 m below top of casing (96.12 m OD) Pumping water level : 18.13 m below top of casing (after 10 hrs continuous pumping) Drawdown : 10.78 m Abstraction rate : 1080 m3/d (9,835 gal/hr) Normal consumption : ~450 m3/d (97,700 gal/d on average, over ~10 hrs) Specific capacity : 90 m3/d/m (pumping test data extrapolated to 1 week) Pumping test summary: (i) abstraction rate : 1073 m3/d (ii) specific capacity : 100 m3/d/m (10 hours) (iii) transmissivity : 105 m2/d [94 – 196 m2/d] 2. METHODOLOGY There were three stages involved in assessing the area: a detailed desk study, site visits and fieldwork, and analysis of the data. The desk study was conducted in the Geological Survey where the subsoil and bedrock geologies were compiled from the original 6" field sheets. Basic public supply well details were recorded by County Council personnel in the form of a questionnaire which included a precise location and any relevant borehole, chemistry and pumping test data available. The second stage comprised site visits and fieldwork in the surrounding area, including a pumping test which was carried out on the public supply well to examine the aquifer characteristics. The area encompassing a 1 km radius around the source was also mapped with regard to subsoil and bedrock geology, hydrogeology and vulnerability to contamination. Finally, two raw water samples were taken in September 1993 and April 1994 for full suites of chemical and bacterial analyses. Stage three, the assessment stage, utilised analytical equations and mapping techniques to delineate protection zones. 3. WELL LOCATION AND SITE DESCRIPTION This source is the main public supply well for Ballyagran and the surrounding area and it is also referred to as the Castletown/Ballyagran or Drewscourt Supply. It is located to the east of the village, in a County Council owned enclosure which is surrounded by a wall and is very well maintained. The wellhead is located outside to 1 the rear of the pumphouse and it lies below ground level. The chamber above the wellhead is protected by way of removable concrete slabs which are slotted in and lie flush with ground level, but which are not locked. 4. TOPOGRAPHY, SURFACE HYDROLOGY AND LAND USE Ballyagran lies to the south of the Corronoher ridge, at a height of approximately 100 m OD. The land surface dips gently to the south-southeast, eventually draining into the River Maigue. The ground is relatively flat and low-lying to the south of the village, while becoming more hummocky to the north. The River Maigue flows in an easterly direction along the county border, collecting drainage from the many surface water courses in the general area. In particular there are two relatively major tributaries in the area of interest, one of which lies to the east, and the other to the west of the village. Surface drainage is absent in the area to the immediate west of the source and is fairly sparse towards the north; the density of drainage ditches increases however, moving towards the south. There are also a number of isolated ponds dispersed amongst the hummocky terrain to the north. Small springs and seeps are numerous to the north and east of the village, and small streams from these trend in all directions to eventually drain into the River Maigue. Excluding the village, the land is primarily used for grazing. 5. GEOLOGY 5.1 Bedrock geology The geology of the area around Ballyagran is dominated by the presence of the west-east trending Rockhill anticline which lies to the east of the village (Fig. 1). The anticline is cored with Kiltorcan Sandstones and these are flanked by the shallow dipping (20°) Mellon House Beds (sandstones, siltstones, shales and limestones), Ringmoylan Shales and Ballysteen muddy limestones, respectively. The public supply borehole was drilled into the Kiltorcan Sandstones which are described from outcrop information further to the east, as coarse grey and yellowish grits, with thin flaggy grey and rusty grits, and shales. 5.2 Subsoils (Quaternary) geology The subsoils present in the immediate vicinity of the source are limestone-dominated gravels, tills and till-with- gravel (Fig. 2). Pits are common in the gravel deposits and there are numerous sections as a result. They show primarily coarse sand grading into fine gravels, with larger rounded to sub-rounded clasts and a dominantly silty matrix. A sample taken in a deposit of till-with-gravel to the north of the site (Sample No. 931009; NGR 14662, 12878; Fig. 3) shows a poorly sorted sub-angular to sub-rounded cobble gravel, in a coarse sandy to gravelly, poorly sorted matrix. Two boreholes were drilled by the GSI (as part of the study) in till-with-gravel to the south of the source, on Door’s farm (NGR 14668, 12742) and at the Co. Co. sewage works, and the deposits found in each were thin sandy units, interbedded with thicker stiff clayey bands. Limestone till is common further to the north, where it is overlain in places with peaty deposits and till-with-gravel. The Ballyagran area lies within the extensive ice marginal deposits in Limerick which stretch from the foot of the Galty Mountains, through south Limerick, and up towards Foynes. The deposits are typically quite thick, reaching 40 m in places, and they comprise a mixture of sands and gravels, silty sands, various tills and stiff clays. With the extensive thicknesses and the chaotic depositional processes which are known to occur at the ice margin, it is inevitable that the deposits will vary with depth. In particular it is expected that there may be sandy gravelly lenses within the till, and clay-rich sediments within the till-with-gravel and the sand and gravel deposits. 5.3 Soils Soils of the area are primarily derived from a parent material of glacial drift origin, mainly limestone with some sandstone, shale and volcanics, and they include members of two of the more common series in Limerick, the Howardstown gleys and the Elton grey brown podzolics. The gleys are found predominantly in the lower lying areas to the south of the source while the Elton podzolics are found on the more gravelly areas to the north and 2 east. There are also some areas further to the north where the brown earths of the Baggotstown series are present and these are derived from limestone-dominated glacial sands and gravels. The soils are shown on the published soils map of Co. Limerick (Finch and Ryan, 1966) and so are not reproduced. 5.4 Depth-to-rock Rock crops out to the east of the source on the Rockhill anticline, indicating that rock is generally close to surface in that region although it is often overlain by a thin covering of limestone till. Depth-to-rock in the public supply borehole is estimated at between 13 and 16 m, based on the depth of casing, and thicknesses appear to increase moving southwards towards the river. A bore on Welsh’s farm for example, approximately 670 m to the east of the creamery, was drilled through more than 33 m of till-with-gravel. The two GSI boreholes went to depths of approximately 11 m and 18 m without reaching bedrock. Deposits to the north are also quite thick; a depth-to-rock of more than 20 m is recorded at the borehole at Kilgobnet House. The depth- to-rock has been contoured for use in compiling the vulnerability map but it is based on relatively few data points and may need refining as further borehole records become available (Fig. 2). 6. HYDROGEOLOGY 6.1 Data availability Hydrogeological data for the Ballyagran area are lacking; the following data sources were used in considering the conceptual model: • Results of a 10 hour drawdown test with four hour recovery which was carried out on the public supply borehole in August 1993 as part of the study. • Data from the County Council files dating back to 1976 when the borehole was drilled. These include a pumping test of more than 72 hours duration, during which the output and the depth of water over the pump (using a pressure gauge) were measured. • A Geoex (a hydrogeological consulting firm) report dated 1975 which was commissioned by the County Council to find a suitable supply of water for the new housing scheme. • GSI well records, although there are few of any significance in the immediate area. • Drillers logs from the two GSI boreholes which were drilled as part of the study. 6.2 Groundwater levels Groundwater levels are difficult to assess as there are few relevant data points. The static water level taken in the public supply well on 13/8/93, following overnight recovery, was 7.35 m below the top of casing (96.12 m OD). A borehole to the north of the site, at Kilgobnet House, has a recorded water level of 12.2 m b.g.l. (~97.5 m OD) but the date of measurement is not known. It is reasonable to assume that both of the relatively major streams are in hydraulic continuity with groundwater; water levels in the streams can therefore be taken as groundwater levels.